The crest factor or peak-to-average ratio (PAR) is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform. In many wireless communication technologies, the communication signals often have a high peak-to-average ratio (PAR) that can impair the efficiency of the power amplifiers (PAs) employed in wireless base stations. A number of techniques have been proposed or suggested for reducing the PAR in order to improve the efficiency of the power amplifier to thereby allow a higher average power to be transmitted before saturation occurs.
Crest Factor Reduction (CFR) is a digital technique used to reduce the PAR of the transmitted wireless signal. Generally, Crest Factor Reduction techniques employ peak detection and then peak cancellation by subtracting a cancellation pulse from the detected peaks, to reduce the peak amplitude and thereby reduce the PAR, The cancellation pulse is pre-computed and has a frequency response that matches the signal/channel spectral response. Thus, by design, the clipping noise is confined inside the signal channel, and does not introduce any noise in adjacent channels or out of band.
In existing multi-standard radio (MSR) multi-channel systems, a base-station first performs channel filtering, up-conversion from a baseband signal, and channel combining in the digital domain. Thereafter, the resulting composite signal undergoes Crest Factor Reduction on the combined signal at a high sampling rate (with significant complexity). The various multiple channels in a given multi-channel system often employ different technologies (with different requirements), such as Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), each potentially having different latency requirements. For example, the narrow bandwidth of GSM requires long filters for pulse cancellation in the CFR which would penalize the LTE channels, for instance, in term of latency and complexity. Thus, the different technologies typically have different latency requirements.
Thus, a need exists for Crest Factor Reduction techniques that can perform Crest Factor Reduction for a plurality of channels employing different technologies with improved latency and reduced complexity.